Dynamics Analysis And Optimization Design For The Valve Train And Belt Transmission Of A Diesel Engine

On the basic of a vehicle high speed four stroke diesel engine, this paper researches the viberation behavior of its valve train and front belt transmission and optimizes their structure, and analyzes stress of the key parts in valve train. It showes that valve train is one of the main noise and viberation source in engine with Noise and Viberaton experiments.About valve train, three kinds of Unsymmetrical cam profiles are used in the cam design for the valve train of a side-mounted camshaft High-speed Diesel engines, which are polydyne, Individual Section Acceleration Curves(ISAC) and polydyne-ISAC. The speed curves and displacement curves of these profies are obtained throughout two-mass kinetic models, and advantages and disadvantages of each one have been found out by the comparisons among their fullness ratios, jerks and max contacting stresses between tappets, etc, turning out the final profile optimization plan. Comparing the optimized profile with the original one in terms of force of valve seating, cam tappets contacting stress, valve acceleration, valve speed and displacement, etc. under dynamic models based on multi-freedom, the optimized one is improved in all the aspects above.With regard to front belt transmission, obtained the results about dynamic connection force between two belt tooth, belt tooth paths and contact forces to pulleys and so on, and illustrated the effects of irreglarities of crankshaft's rotary speed and other driving torques on the dynamics characteristics of synchronous belt,by studying with the characteristics of synchronous belt dynamics using Multi-body Dynamics of a Diesel engines. After the analysis, it is found that the effect of irregularities of crankshaft's rotary speed on the vibrations of synchronous belt in the linear and transversal orientations are dominate. Comparing the original timing system and the one optimized, it is found that the inherence frequency of synchronous belt depends on its span. Therefore it is important to reasonably control the span of belt and the location of tensioner pulley for timing system design.In stress analysis of camshaft and valve springs, direct intergration method for transient stress calculation is mainly introduced and several notice for finite element griding in stress calculation are given, which indicates that the dispalcement of each cam is more important than camshaft stress. For valve spring, nonlinear spring design method is introduced and the characters of spring being pressed are analyzed. In calculation for springs stiffness, the results of linear approximation method, nonlinear calculation and finite element calculation are compared, which shows that in the dynamic analysis of valve train, regarding the spring stiffness as a linear multi-quality model could obtain the required accuracy for calculation.The paper developed the related new method and technical process in the valve train and front belt transmission from analysis view of engineering application. Gained a series of results for practical engineering value, which can instruct engineering significantly.